Comparison of the outcomes of trabeculectomy and Ab interno trabeculotomy on corneal biomechanics

Abstract

This observational cohort study aimed at comparing the postoperative changes in corneal biomechanical properties between trabeculectomy and ab interno trabeculotomy. The study included 46 eyes undergoing trabeculectomy (TLE group) and 92 eyes undergoing ab interno trabeculotomy with lens reconstruction (µLOT + LR group). Corneal hysteresis (CH), which represents corneal damping capacity, along with stiffness parameter A1 (SP-A1) and stress-strain index (SSI), which represent corneal stiffness, were measured preoperatively using the Ocular Response Analyzer and Corneal Visualization Scheimpflug Technology (Corvis ST), respectively. Changes in these parameters 12 months after surgery were analyzed and compared between the groups. Baseline IOP and biomechanical parameters were comparable between both groups. Both surgeries significantly reduced IOP after 12 months, with a greater reduction in the TLE group than in the µLOT + LR group (- 7.4 vs. -3.8 mmHg). Corvis ST parameters showed significant changes postoperatively, with greater reductions in SP-A1 and SSI in the TLE group. CH increased significantly in both groups, but the ratio of the change in CH to the change in IOP (ΔCH/ΔGAT-IOP) was greater in the µLOT + LR group. In conclusions, the cornea exhibited greater softening following TLE compared to µLOT + LR, suggesting a more substantial reduction in IOP. Clinicians should consider the potential bias for IOP measurement due to corneal softening. In contrast, the increase in CH per reduction in IOP was more pronounced after µLOT + LR. These findings highlight the importance of recognizing surgery-induced biomechanical changes when interpreting postoperative IOP measurements, as well as their potential role in predicting long-term glaucoma progression.

Fig. 1

From top to bottom, corneal movements captured by Corvis ST. Initially, the cornea is in its natural and undeformed state. An air puff is applied, leading to the first applanation wherein the cornea is flattened. The cornea then reaches its highest concavity wherein it is maximally indented. Finally, the cornea undergoes a second applanation as it reverts to its original form.